MORE ABOUT STATIC NAT
- STATIC NAT involves statically configuring one-to-one mappings of PRIVATE IP ADDRESSES to PUBLIC IP ADDRESSES
- When traffic from the INTERNAL HOST is sent to the OUTSIDE NETWORK, the ROUTER will translate the SOURCE ADDRESS
- HOWEVER, this one-to-one mapping also allows EXTERNAL HOSTS to access the INTERNAL HOST via INSIDE GLOBAL ADDRESS
DYNAMIC NAT
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In DYNAMIC NAT, the ROUTER dynamically maps INSIDE LOCAL ADDRESSES to INSIDE GLOBAL ADDRESSES, as needed
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An ACL is used to identify WHICH traffic should be translated
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If the SOURCE IP is PERMITTED; the SOURCE IP will be translated
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If the SOURCE IP is DENIED; the SOURCE IP will NOT be translated
💡 However, Packet Traffic will NOT be dropped
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A NAT POOL is used to define the available INSIDE GLOBAL ADDRESS
- Although they are dynamically assigned, the mappings are still one-to-one (one INSIDE LOCAL IP ADDRESS per INSIDE GLOBAL IP ADDRESS)
- If there are NOT enough INSIDE GLOBAL IP ADDRESSES available (=ALL are being used), it is called ‘NAT POOL EXHAUSTION’
- If a PACKET from another INSIDE HOST arrives and needs NAT but there are no AVAILABLE ADDRESSES, the ROUTER will drop the PACKET
- The HOST will be unable to access OUTSIDE NETWORKS until one of the INSIDE GLOBAL IP ADDRESSES becomes available
- DYNAMIC NAT entries will time out automatically if not used, or you can clear them manually
NAT POOL EXHAUSTION
192.168.0.167 TIMES OUT and 192.168.0.98 is assigned it’s TRANSLATED SOURCE IP
DYNAMIC NAT CONFIGURATION
show ip nat translations
DYNAMIC PAT (NAT OVERLOAD)
- PAT (NAT OVERLOAD) translates BOTH the IP ADDRESS and the PORT NUMBER (if necessary)
- By using a unique PORT NUMBER for each communication flow, a single PUBLIC IP ADDRESS can be used by many different INTERNAL HOSTS
- PORT NUMBERS are 16 bits = over 65,000 available port numbers
- The ROUTER will keep track of which INSIDE LOCAL ADDRESS is using which INSIDE GLOBAL ADDRESS and PORT
PAT CONFIGURATION (POOL)
show ip nat translations
PAT CONFIGURATION (INTERFACE)
show ip nat translations
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